The present invention directed to a coating process for a dual-layer coating on a suspension component for an automobile; and more particularly, for suspension spring components.
Steel suspension components for use with automobile suspension systems are typically coated with a protective coating to protect the components from corrosion and other environmental damage. Because these components are typically subject to impact damage caused by flying stones and gravel,the automotive industry is beginning to utilize dual-layer coating systems for such suspension components, where the first layer is a zinc-rich coating that has a self-healing property when the coating is broken or damaged and an outer layer of a thermoplastic material that protects the inner layer from chipping and damage caused by objects thrown up from the road. The inner, zinc-rich layer is typically approximately 2.00 to approximately 3.00 mils and the outer coat thermoplastic layer is typically approximately 13.0 to approximately 17.0 mils. See U.S. Pat. No. 5,981,086 for more detailed information regarding the dual-coat materials.
Traditionally, the zinc-rich layer has been applied to the steel suspension component utilizing an electrostatic spray application (involving the steps of charging the zinc-rich powder with a low amp, very high voltage charge, placing the steel components on a grounded conveyor, and then spraying the components with the charged powder such that the charged powder is evenly and uniformly attracted to, and hence, applied to the grounded steel component). After the electrostatic spray application, the component is conventionally placed in an oven so that the layer of zinc-rich powder is baked onto the steel component (i.e. is cured). It is then envisioned that the outer, thermoplastic layer will be applied in a similar manner.
A problem confronted by the industry with this dual-coat process is that the thermoplastic powder is not sufficiently conductive (not electrostatic), and hence, utilizing an electrostatic coating operation for the outer, thermoplastic layer has been very problematic. The coating industry has, thus, resorted to different types of dual-layer coatings and has experimented with different types of methods for coating the outer layer. The primary problem with these alternate methods for applying the outer, thermoplastic coat is that they require a labor-intensive, manual application and are therefore very expensive to perform.
The application problems are increased with automotive components having more complex shapes, such as coil-springs. Prior-art attempts for obtaining an adequate thickness and uniformity of the thermoplastic layer on both the inner and outer diameter surfaces of the coil-spring have included over-heating the coil-spring prior to a spray application of the thermoplastic powder in an attempt to make the thermoplastic powder attract to and adhere to the inner and outer diameter surfaces of the coil-spring (i.e., relying more on the heat of the coil-spring to attract the thermoplastic powder than the electro-static properties). A problem with this attempt is that such over-heating causes the zinc-rich layer to become over-cured, which, in-turn, substantially reduces the amount of adhesion or bonding between the zinc-rich layer and the thermoplastic layer in the finished product. Additionally, in an attempt to obtain adequate thickness and uniformity on the inner diameter surfaces of the coil-spring, the outer diameter surfaces tend to become overloaded with the thermoplastic material. This increases consumption of the thermoplastic powder (increases cost) and presents possible fit problems with mating components during automobile assembly.
Accordingly, there is a need for a high-volume process for applying the dual-layer coating described above to steel suspension components that does not necessitate the use of an error-prone electrostatic spray application for the outer, thermoplastic layer of the dual-layer coating.
The present invention involves a process for applying a dual-layer protective coating to metallic suspension components of an automobile that involves the steps of applying a first coat of the zinc-rich coating powder utilizing the conventional electrostatic application process; partially curing the layer of zinc-rich coating that has been applied to the steel component such that the zinc-rich coating is gelled; immersing the component with the first layer of gelled zinc-rich coating in a fluidized bed of the thermoplastic powder so that a relative uniform layer of the thermoplastic coating powder is applied over the first coat of gelled zinc-rich coating; and finally curing the outer layer of thermoplastic powder coating and the inner layer of the zinc-rich coating.
In an exemplary embodiment, the fluidized bed of the thermoplastic powder is heated to bring the fluidized bed of thermoplastic powder within a predetermined temperature difference from the temperature of the component with just prior to the component being immersed within the fluidized bed of thermoplastic powder. In an even more detailed embodiment, the temperature of the component prior to being immersed within the thermoplastic powder and the temperature of the fluidized of thermoplastic are monitored prior to immersing the component within the fluidized bed of thermoplastic powder; and further, the heat of the fluidized bed of thermoplastic powder may be adjusted if the difference between the component and the fluidized thermoplastic deviate from the predetermined potential.
In yet a further detailed embodiment, excess thermoplastic powder is removed from the components subsequent to immersing the components within the fluidized bed of thermoplastic powder by the step of directing a stream of air or gas against the excess powder carried on the components.
Therefore, it is a first aspect of the present invention to provide a method for applying a protective coating to a steel component of a vehicle that includes the steps of: applying a first coat of epoxy-based, protective powder to the component; partially curing the first coat; heating a fluidized bed of thermoplastic powder; immersing the component with the partially cured first coat into the heated fluidized bed of thermoplastic powder so as to apply a second coat of the thermoplastic powder over the first coat; withdrawing the component from the fluidized bed; and finally curing the first and second coats. In a detailed embodiment the fluidized bed of thermoplastic powder is heated to bring the fluidized bed of thermoplastic powder within a predetermined temperature difference from the temperature of the component at a time just prior to the immersing step. In a further detailed embodiment, the method further includes the steps of: monitoring the temperature difference between the fluidized bed of thermoplastic powder and the component at the time just prior to the immersing step; and responsive to the monitoring step, adjusting at least one of the temperature of the fluidized bed of thermoplastic powder and the temperature of the component at the time just prior to the immersing step. In yet a further detailed embodiment, the adjusting step is performed automatically; or, alternatively, the adjusting step is performed, at least in part, manually.
In an alternate detailed embodiment of the first aspect of the present invention, the predetermined temperature difference is approximately 60xc2x0 F. to approximately 75xc2x0 F. In another alternate detailed embodiment of the first aspect of the present invention, the temperature of the component at the time just prior to the immersing step is approximately 140xc2x0 F. to approximately 230xc2x0 F. and the temperature of the fluidized bed of thermoplastic powder is approximately 90xc2x0 F. to approximately 180xc2x0 F. In a further detailed embodiment, the temperature of the component at the time just prior to the immersing step is approximately 200xc2x0 F. to n approximately 210xc2x0 F. and the temperature of the fluidized bed of thermoplastic powder is approximately 135xc2x0 F. to approximately 145xc2x0 F.
In an alternate detailed embodiment of the first aspect of the present invention, the partially curing step includes the step of heating the component with the first coat applied thereto in an oven at a predetermined temperature for a predetermined period of time. In a further detailed embodiment, the method further includes the steps of: monitoring a sum of the oven temperature and the temperature of the fluidized bed of thermoplastic powder; and maintaining the sum of the oven temperature and the temperature of the fluidized bed of thermoplastic powder within a predetermined temperature range. In yet a further detailed embodiment, the maintaining step includes the step of responsive to the monitoring step, adjusting at least one of the oven temperature and the temperature of the fluidized bed of thermoplastic powder. In an alternate detailed embodiment, the predetermined temperature range is approximately 430xc2x0 F. to approximately 455xc2x0 F.
In another alternate detailed embodiment of the first aspect of the present invention, the method further includes the step of monitoring a sum of the component temperature at the time just prior to the immersing step and the temperature of the fluidized bed of thermoplastic powder; and maintaining the sum of the component temperature at the time just prior to the immersing step and the temperature of the fluidized bed of thermoplastic powder within a temperature range. In a further detailed embodiment, the maintaining step includes the step of responsive to the monitoring step, adjusting at least one of the oven temperature and the temperature of the fluidized bed of thermoplastic powder. In a further detailed embodiment, the predetermined temperature range is approximately 325xc2x0 F. to approximately 340xc2x0 F.
In another alternate detailed embodiment of the first aspect of the present invention the step of heating the fluidized bed of thermoplastic powder includes the steps of injecting a gas into the fluidized bed heating the gas prior to the injecting step. In a further detailed embodiment, the injecting step also performs, at least in part, the step of fluidizing the thermoplastic powder contained within the bed.
In another alternate detailed embodiment of the first aspect of the present invention the step of heating the fluidized bed of thermoplastic powder includes the step of repeatedly immersing heated components into the fluidized bed of thermoplastic powder. In a further detailed embodiment, the step of heating the fluidized bed of thermoplastic powder includes the step of repeatedly immersing groups of the heated components into the fluidized bed of thermoplastic powder.
In another alternate detailed embodiment of the first aspect of the present invention, the step of heating the fluidized bed of thermoplastic powder includes the steps of injecting a gas into the fluidized bed, heating the gas prior to the injecting step and repeatedly immersing groups of the heated components into the fluidized bed of thermoplastic powder.
In another alternate detailed embodiment of the first aspect of the present invention, the heating step includes the step of pre-heating the fluidized bed of thermoplastic powder and the method further includes the step of maintaining the fluidized bed of thermoplastic powder at a predetermined temperature range. In a further detailed embodiment, the predetermined temperature range is dependent, at least in part, upon the temperature of the component at a time just prior to the immersing step. In an alternate detailed embodiment, the partially curing step includes the step of heating the component with the first coat in an oven for a predetermined period of time; and during the preheating step, the temperature of the oven is adjusted according, at least in part, to the temperature of the fluidized bed of thermoplastic powder. In an alternate detailed embodiment, the pre-heating step pre-heats the fluidized bed of thermoplastic powder to a temperature of approximately 90xc2x0 F. to approximately 180xc2x0 F.
In another alternate detailed embodiment of the first aspect of the present invention, the method further includes the step of, during or after the withdrawing step, removing excess of the thermoplastic powder from the component. In a further detailed embodiment, the removing step includes the step of directing at least one stream of gas against the component.
In another alternate detailed embodiment of the first aspect of the present invention, the first coat of epoxy-based, protective powder is a zinc-rich epoxy-based, protective powder.
In another alternate detailed embodiment of the first aspect of the present invention, each of the steps are respectively performed in stages on a group of the components. In a further detailed embodiment the method further includes the step of sequentially delivering multiple groups of the components to the respective stages. In yet a further detailed embodiment, the delivering step is performed, in most part, by a conveyor system.
It is a second aspect of the present invention to provide a batch method for applying a protective coating to multiple groups of metallic components for a vehicle that includes the steps of: applying a first coat of epoxy-based, protective powder to a group of the components at a first coat station; partially curing the first coat on the group of the components at a gelling station; pre-heating a fluidized bed of thermoplastic powder; immersing the group of the components with the partially cured first coat into the pre-heated fluidized bed of thermoplastic powder so as to apply a second coat of the thermoplastic powder over the first coat at a second coat station; and finally curing the first and second coats on the group of components, at least in part, at a curing station. In a further detailed embodiment, the fluidized bed of thermoplastic powder is pre-heated to bring the fluidized bed of thermoplastic powder within a predetermined temperature difference from the temperature of the group of components as detected between the gelling station and the second coat station. In a further detailed embodiment, the batch method further includes the steps of: monitoring the temperature difference between the fluidized bed of thermoplastic powder and the group of components as detected between the gelling station and the second coat station; and responsive to the monitoring step, adjusting at least one of the temperature of the fluidized bed of thermoplastic powder and the temperature of the group of components as detected between the gelling station and the second coat station. In yet a further detailed embodiment, the adjusting step is performed automatically; or is performed, at least in part, manually. In an alternate detailed embodiment, the predetermined temperature difference is approximately 60xc2x0 F. to approximately 75xc2x0 F.
In an alternate detailed embodiment of the second aspect of the present invention, the temperature of the component between the gelling station and the second coat station is approximately 140xc2x0 F. to approximately 230xc2x0 F. and the temperature of the fluidized bed of thermoplastic powder is approximately 90xc2x0 F. to approximately 180xc2x0 F. In a further detailed embodiment, the temperature of the component between the gelling station and the second coat station is approximately 200xc2x0 F. to approximately 210xc2x0 F. and the temperature of the fluidized bed of thermoplastic powder is approximately 135xc2x0 F. to approximately 145xc2x0 F.
In an alternate detailed embodiment of the second aspect of the present invention, the gelling station utilizes a gelling oven at a predetermined temperature for a predetermined period of time. In a further detailed embodiment, the batch method further includes the steps of: monitoring a sum of the gelling oven temperature and the temperature of the fluidized bed of thermoplastic powder; and maintaining the sum of the gelling oven temperature and the temperature of the fluidized bed of thermoplastic powder within a predetermined temperature range. In yet a further detailed embodiment, the maintaining step includes the step of responsive to the monitoring step, adjusting at least one of the gelling oven temperature and the temperature of the fluidized bed of thermoplastic powder. In an alternate detailed embodiment, the predetermined temperature range is approximately 435xc2x0 F. to approximately 455xc2x0 F. In another alternate detailed embodiment, the batch method further includes the steps of: monitoring a sum of the temperature of the group of components between the gelling station and the second coat station and the temperature of the fluidized bed of thermoplastic powder; and maintaining the temperature sum within a predetermined temperature range. In a further detailed embodiment, the maintaining step includes the step of, responsive to the monitoring step, adjusting at least one of the gelling oven temperature and the temperature of the fluidized bed of thermoplastic powder. In yet a further detailed embodiment, the predetermined temperature range is approximately 325xc2x0 F. to approximately 340xc2x0 F.
In another alternate detailed embodiment of the second aspect of the present invention, the step of pre-heating the fluidized bed of thermoplastic powder includes the steps of injecting a gas into the fluidized bed and heating the gas prior to the injecting step. In a further detailed embodiment, the injecting step also performs, at least in part, the step of fluidizing the thermoplastic powder contained within the bed.
In another alternate detailed embodiment of the second aspect of the present invention, the step of pre-heating the fluidized bed of thermoplastic powder includes the step of repeatedly immersing groups of heated components into the fluidized bed of thermoplastic powder.
In another alternate detailed embodiment of the second aspect of the present invention, the step of pre-heating the fluidized bed of thermoplastic powder includes the steps of injecting a gas into the fluidized bed, heating the gas prior to the injecting step, and repeatedly immersing groups of the heated components into the fluidized bed of thermoplastic powder.
In another alternate detailed embodiment of the second aspect of the present invention, the batch method further includes the step of maintaining the fluidized bed of thermoplastic powder at a predetermined temperature range. In a further detailed embodiment, the predetermined temperature range is dependent at least in part, upon the temperature of the group of components between the gelling station and the second coat station. In an alternate detailed embodiment, the partially curing step includes the step of heating the group of components with the first coat in a gelling oven for a predetermined period of time and, during the pre-heating step, the temperature of the gelling oven is adjusted according, at least in part, to the temperature of the fluidized bed of thermoplastic powder.
In another alternate detailed embodiment of the second aspect of the present invention, the pre-heating step pre-heats the fluidized bed of thermoplastic powder to a temperature of approximately 90xc2x0 F. to approximately 180xc2x0 F.
In another alternate detailed embodiment of the second aspect of the present invention, the batch method further includes the step of removing excess of the thermoplastic powder from the component. In a further detailed embodiment, the removing step is performed at, or immediately after, the second coat station. In yet a further detailed embodiment, the removing step includes the step of directing at least one stream of gas against the component.
In another alternate detailed embodiment of the second aspect of the present invention, the first coat of epoxy-based, protective powder is a zinc-rich epoxy-based, protective powder.
It is a third aspect of the present invention to provide a method for applying a thermoplastic, protective coat to an automotive component that includes the steps of heating the automotive component; heating a fluidized bed of thermoplastic powder to be within a predetermined temperature difference from the heated automotive component; and immersing the heated automotive component within the heated fluidized bed of thermoplastic powder. In a detailed embodiment, the predetermined temperature difference is approximately 60xc2x0 F. to approximately 75xc2x0 F. In yet a further detailed embodiment, the temperature of the automotive component is approximately 200xc2x0 F. to approximately 210xc2x0 F. and the temperature of the fluidized bed of thermoplastic powder is approximately 135xc2x0 F. to approximately 145xc2x0 F.
It is a fourth aspect of the present invention to provide a method for applying a dual-layer protective coating to a steel component of a vehicle that includes the steps of: applying a first coat of epoxy-based, protective powder to the component; partially curing the first coat on the component in an oven at a first temperature; immersing the component with the partially cured first coat in a fluidized bed of thermoplastic powder heated at a second temperature to provide a second coat on the component; finally curing the first and second coats on the component; and repeating the applying, partially curing, immersing and finally curing steps for a plurality of the components while controlling the thickness of the second coat by maintaining a sum of the first and second temperatures within a predetermined temperature range. In a further detailed embodiment, the maintaining step includes the steps of detecting the first temperature, detecting the second temperature, and adjusting at least one of the first and second temperatures if the sum of the first and second temperatures falls outside of the predetermined temperature range. In yet a further detailed embodiment, the detecting and adjusting steps are automatic; or, alternatively, the adjusting step is manual.
In an alternate detailed embodiment of the fourth aspect of the present invention, the predetermined temperature range is approximately 435xc2x0 F. to approximately 455xc2x0 F., achieving a seconds coat thickness of approximately 13 mils to 17 mils. In a further detailed embodiment, the first temperature is approximately 300xc2x0 F. to approximately 350xc2x0 F. and the second temperature is approximately 135xc2x0 F. to approximately 145xc2x0 F.
It is a fifth aspect of the present invention to provide a method for applying a protective coating to a metallic component of a vehicle that includes the steps of: applying a first coat of epoxy-based, protective powder to the component; immersing the component with the partially first coat into the heated fluidized bed of thermoplastic powder so as to apply a second coat of the thermoplastic powder over the first coat; withdrawing the component from the fluidized bed; during or after the withdrawing step, actively removing excess thermoplastic powder from the component; and finally curing the first and second coats. In a detailed embodiment, the step of actively removing excess thermoplastic powder from the component includes the step of directing at least one stream of gas against the component.